Self-assembly of amphiphilic β-sheet peptide tapes based on aliphatic side chains

Amphiphilic β-sheet nanotapes based on the self-assembly of 9mer and 7mer de novo designed β-strand peptides were studied in the dilute regime. The hydrophobic face of the tapes consisted predominantly of aliphatic (leucine) side chains, while the hydrophilic tape face contained polar side chains (glutamine, arginine and glutamic acid). Both peptides underwent a transition from a monomeric random coil to a self-assembled β-sheet tape upon increase of peptide concentration in aqueous solutions. P(9) -6 exhibited lower critical concentration (c*) for self-assembly and thus higher propensity for self-assembly in water, compared to the shorter P(7) -6. At neutral pH where there was little net charge per peptide, self-assembly was favoured compared to low pH in which there was a net + 1 charge per peptide; the net charge decreased overall intermolecular attraction, manifested as an increase in c* for self-assembly in low compared to neutral pH aqueous solutions. Propensity for self-assembly and β-sheet formation was found to be greatly enhanced in a polar organic solvent (methanol) compared to water. These studies combined with future more extensive comparative studies between amphiphilic tapes based on aliphatic amino acid residues and amphiphilic tapes based on aromatic residues will throw more light on the relative importance of hydrophobic versus aromatic interactions for the stabilisation of peptide assemblies. Systematic studies of this kind may also allow us to throw light on the fundamental principles that drive peptide self-assembly and β-sheet formation; they may also lead to a set of refined criteria for the effective design of peptides with prescribed combination of properties appropriate for specific applications.